Positive head for high-intensity arc lamps



2 Shets-Sheet l INVENTOR ATTORNEY5 April 9, 1957 GRETENER POSITIVE HEAD FOR HIGH-INTENSITY ARC LAMPS Filed Dec; 11, 1953 BY 7 //M April 9, 1957 E. GRETENER POSITIVE HEAD FOR HIGH-INTENSITY ARC LAMPS Filed Dec. 11, 1953 2 Sheets-Sheet 2 Enem 612mm I NVENTOR.

United States Patent POSITIVE HEAD FOR HIGH-INTENSITY ARC LAMPS Edgar Gretener, Zurich, Switzerland Application December 11, 1953, Serial No. 397,749

Claims priority, application Switzerland December 20, 1952 Claims. Cl. 313-36) The present invention relates to a positive head for high-intensity are lamps.

In high-intensity are. lamps the positive head serves to guide the positive carbon in such a manner that its position is correctly centered with respect to the illumination system and to supply the arc current to the carbon. In blown are lamps furthermore the positive head contains anozzle for the air jet, which, as is well known, serves to concentrate are discharge and tail flame into the space in front of the positive crater.

When high-intensity arc lamps are operated at high current densities it is necessary to connect the are current as near as possible to the tip of the electrode. At the same time the positive-head must possess good thermal eonductibility to effect cooling of the carbon shell in order to prevent unnecessary heating and oxidation of the carbon'shell or premature evaporation of the luminous substances contained in the carbon core. Generally liquid cooling of the positive head is provided which at the same time prevents excessivethermal stress of the carbon guides, and particularly, of the current contacts.

The present invention is directed to a positive head for high-intensity are lamps and is characterized by two movable contact jaws and a carbon guide fixed to the housing, wherein the contact jaws serving for current admission and cooling are disposed as near as possible to the arcing end and have the form of air jet nozzles, whereas the carbon guides, serving to center the carbon fed from the rear with respect to the optical system, are located behind the contact jaws, andwherein the contact jaws are movably supported in radial direction with respect to the carbon, so that their contact surfaces embrace the carbon from all sides under pressure without disturbing centering of the carbon in the carbon guides.

The optical system referred to above may be of the character of that described in Figure 2 of U. 8. Patent No. 2,621,284 to which reference is made by way of example. The particular character of the optical system is not critical in the present combination and it is included here to clarify the function of the positive head. A carbonate will radiate freely into space in substantially all directions unless some optical system is used. Where an optical system is employed, as is the case in any motion picture projector, search light or similar light focusing structure using a carbon arc source, the positivehead serves, among other purposes, tocenter the positive carbon with respect to the optical system. To achieve this result the carbon guides are fixedly mounted with respect to the optical system. The eontact jaws do not interfere with the action of the carbon guides'because they are floating. This arrangement comr 2,788,459 Cg iatented Apr. 9, 1957 Figs. 2 and 3 show the same embodiment in plan view and in different sections.

Pig. 4 is a side elevation showing one form of optical system embodying the invention.

As shown in Fig. l, the are I is struck between the crater 2 of the positive carbon 3 and the negative carbon 4. An air jet 5 having the form of the concentric hollow cone converging in direction towards the negative carbon, is directed from the rear to the arcing end of the positive carbon, this jet concentrates arc discharge and tail fiame into the cylindrical space in front of the positive crater. The evaporation and oxidation products from the are led along by the air are received by an air duct 6 and exhausted from the lamp.

The radiation originating from positive crater and the gas column located in front thereof impinges upon an illumination system (not shown in the drawing), by way of example, a concave reflector or a condenser lens. In order to embrace as completely as possible the light flux issuing from the are, a concave reflector is customarily employed, which in the representation would be located to the right of the negative carbon, so that the positive head is located within the light beam issuing from such a reflector and directed from right to left.

The positive carbon 3 is guided in the positive head. According to the invention its essential parts are two movable contact jaws 1t) and 11 and a fixed carbon guide 12, i. e. stationary with respect to the housing. The contact jaws serve for current supply and for cooling and are located as near as possible to the arcing end. On their foremost part they furthermore support the blower nozzles 13 from which air jet 5 issues. The carbon guide 12 located behind the contact jaws serves to center the carbon with respect to the optical system. With the optical systems employed today, as is well known, centering must be effected with high accuracy as any deviation will cause de-foeussing of the light spot produced on the object to be illuminated and will consequently entail poor illumination and loss of light. According to representation a prism-shaped rail is employed as carbon guide, against which carbon 3 is urged by a spring 14. The carbon is continuously advanced in a well known manner by the transport rolls 15, which are rotated by a source of energy not shown, which in its turn is actuated, e. g. in well known manner, by a photoelectric control so that the crater 2 is constantly kept at the focus of the optical system. Devices of this kind are well known. it is obvious that in place of a single prismshaped guide rail several separate guide rails may be employed, to ensure reliable centering of the carbon. Preferably steatite or a material with a similarly low friction coefficient is employed for the guide.

The contact jaws are urged against the carbon by spring pressure. Their inner surfaces embrace the carbons as completely as possible thereby ensuring good current transmission to the carbon. Suspension of the contact jaws furthermore permits displacement in radial directione. g. at right angles to the axis of the carbonso that they may easily adapt to the position of the carbon without impairing centering of the carbon in the carbon guide. Floating and self-centering suspension of the jaws is obtained by means of a fork, the two prongs 18 which urge jaws lit and 11 from both sides towards the carbon. The necessary force is derived from a spring 19. lressure blocks 20 are located at the tip of the prongs which may be given a beaded form to permit radial movement of the jaws as mentioned above, they prevent, however, disengagement of the jaws when the carbon is removed or shifting of the jaws in direction of the carbon. In Fig. 1 parts of the front prong 18 have been cut away to show the carbon guide. Prongs 18 are now pivoted on a support 21 fixed to the lamphouse,

cool jaws and carbon sufficiently, liquid cooling is preferably employed.

Three pairs of ducts 22, 23, 24 serve to supply curi rent, cooling agent and blower air to the jaws. These ducts are likewise located within the shadow cone thrust by the jaws and are flexible in order not to hinder displacement of the jaws. By ways of example, metal hose may be employed for the ducts as re resented in Fig. l, or metal bellows tubes as shown in Fig. 2. The flexible connections conducting the cooling agent and the blower arr may at the same time be employed to supply the current, so that separate current connections to the movable aws are not necessary. This has been represented in Fig. l where lead 25 is directly connected to the fixed support part 21. In this case the support may have to be insulated with respect to the lamphouse.

Fig. 2 represents a plan view of the embodiment shown by Fig. 1 partly in section, identical parts being given identical reference numerals. A ring-shaped bore 30 located within the contact jaws supplies air to openings 31. from which the jet issues. Blower air is supplied to bore 30 by tube 23. The cooling liquid is con tained in the rearward chambers 33, and is admitted by duct 22 and led away by a duct 24. Contact pieces 35 are attached to the inside of the jaws, consisting of highly conductive material, e. g. of silver. The contact pieces are mounted to the jaws in a manner ensuring good therrnal transition to the cooling agent. As the contact pieces are subject to wear during operation they are preferably replaceable. If necessary the rear surfaces of the contact pieces may be in immediate contact with the cooling liquid. In this case no separate inner wall 36 of the jaws is necessary.

Fig. 3 shows a section through the positive head along lines AA and BB. Fig. 3 shows that the contact jaws with their contact pieces 35 firmly grip carbon 3 from both sides, the carbon being centered by guide 12. The flow of the coding agent through the chambers is indicated by arrows 37.

According to representation prongs 18 and tension spring 19 support contact jaws and urge them towards the positive carbon from both sides. At the same time they permit radial movement of the jaws. It is likewise possible to obtain support and pressure for jaws by suitably forming the ducts 22, 23, 24. Instead of employing flexible ducts, e. g. metal hoses or bellows tubes, the tubes are rigid and consist of resilient material. They are mounted under tension to product the necessary pressure for the jaws. By a suitable e. g. rectangular cross-section of the tubes it is possible to obtain spring action only in that direction desired for movement of the jaws. In this case the fork construction shown in the drawing is not necessary.

The assembly of Figure 4 shows an optical system embodying the invention. Reflector 51 is held in position by support 50 and mounting 54. The rays of arc 1 are reflected as shown at 52 and 53.

An arrangement according to the present invention offers great advantages with respect to the constructions hitherto known. Structural separation of current connection, cooling and blower nozzle from the centering of the carbon prevents wear of the carbon holder and of the contact impairs the accuracy of centering. In many of the constructions hitherto known, wherein carbon guide and current admission form a structural entity, electrolytical or other efiects add to the purely mechanical wear. After longer periods of operation this wear entails lateral deviation of the carbon from its accurate position. Centering of the carbon by a carbon guide separate from the carbon head and fixed to the lamphouse avoids these deficiencies and ensures its accurate position with respect to the optical system. Division of the positive holder into two movable jaws and the absence of separate contact pieces sliding in slots prevents choking and wedging of the carbon or of the contact pieces in their slot by pulverized material. Current supply and cooling of the carbon is efiected in immediate neighbourhood of the arcing end, so that losses and heating by the current are minimized and oxidation or evaporation of the carbon and the luminous substances is avoided. Cooling of the jaws at the same time prevents burning of the parts of the holder, particularly of the blower nozzle as good heat transition from all parts to the cooling agent exists. By arranging all ducts and support means within the shadow cone of the jaws any additional loss of light is avoided to an exceptional degree. This is very advantageous if such a lamp cooperates with a concave reflector, the positive head being located within the light beam issuing from the reflector. If the lamp is designed for continuous operation for which purpose new carbons are continuously fed from the rear, it is particularly advantageous that no additional fixations or clamps are necessary for holding and advancing the carbon. A positive head according to the present invention thus offers particular advantages in lamps for continuous operation with reflector optics.

While there has been described above a form of the invention which is at present believed to be the preferred form, variations thereof will suggest themselves to those skilled in the art in the light of the above disclosure. All such variations as fall within the true spirit of the invention are intended to be comprehended within the generic terminology of the appended claims.

I claim:

1. A positive head for high-intensity are lamps having an optical system, comprising two contact jaws and a carbon guide, said carbon guide being fixedly mounted with respect to the optical system of the lamp and serving to center the positive carbon sliding in said guide with respect to said system, said contact jaws embracing the carbon under pressure as near as possible to the tip of the positive carbon and being movably supported in a manner to permit displacement in radial direction with respect to the axis of the carbon, so that they do not impair centering of said carbon, said guide being located at the rear of said jaws.

2. A positive head for high-intensity arc lamps having an optical system, comprising two contact jaws, a carbon guide and support means, said jaws and said guide being mounted on said support means, said carbon guide being fixed with respect to the optical system of the lamp and serving to center the positive carbon with respect to said system, said contact jaws being movably supported in a manner to permit displacement in radial direction with respect to the axis of the carbon, so that they do not impair centering of said carbon, said jaws embracing the carbon under pressure as near as possible to the tip of the positive carbon and said guide being located at the rear of said jaws, said support means being located substantially within the shadow cone of said jaws.

3. A positive head as claimed in claim 2, comprising two contact jaws, a carbon guide and support means, said jaws and said guide being mounted on said support means, said carbon jaws serving for current admission, cooling and having the form of air jet nozzles, and being fixedly mounted with respect to the optical system of the lamp and serving to center the positive carbon sliding in said guide with respect to said system, said contact jaws being movably supported in a manner to permit displacement in radial direction with respect to the axis of the carbon, so that they do not impair centering of said carbon, said jaws embracing the .carbon under pressure as near as Possible to the tip of the positive carbon and said guide being located at the rear of said jaws and flexible connections between said jaws and said support part, serving to supply current, cooling agent and blower air, said support part and said connections being substantially disposed within the shadow cone of the jaws.

4. A positive head as claimed in claim 3, wherein said flexible connections supplying cooling agent or blower air at the same time serve as current leads.

5. A positive head as claimed in claim 3, wherein said connections serving to supply cooling agent or blower air are of resilient design, so that they may provide the spring tension necessary for urging the contact jaws.

6. A positive head as claimed in claim 3, wherein said contact jaws are held by the prongs of a fork which urge said jaws from both sides towards said positive carbon, said prongs being pivoted on said support means and permitting displacement of said jaws in radial direction with respect to the carbon axis.

7. A positive head as claimed in claim 3, wherein the surfaces of said jaws contacting said positive carbon are replaceable.

8. A positive head as claimed in claim 7, wherein said replaceable contact surfaces are in immediate contact with the cooling agent circulating through said jaws.

9. A positive head for high intensity are lamps, comprising two contact jaws and a positive carbon guide, said guide having means for mounting in a fixed posi tion and serving to center a positive carbon, said contact jaws constructed to embrace a positive carbon closely adjacent the tip thereof and being movably supported for radial displacement with respect to the carbon axis.

10. The combination set forth in claim 9, support means for said carbon guide, said guide being positioned on the side of said jaws removed from the arc and said support means being of such size and shape that it is positioned substantially within the shadow cone of said aws.

No references cited. 

